Phthalocyanine compounds are useful as coatings, printing inks, catalysts or electronic materials. In recent years, they have been extensively studied particularly for their use as electrophotographic photoreceptor materials, optical recording materials and photoelectric conversion materials.
It is known that phthalocyanine compounds generally exhibit several different crystal forms depending on the process of production or the process of treatment and that the difference in crystal form has a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable p-form. These crystal forms are known capable of interconversion by mechanical strain application, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, and the like (see, for example, U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989). Further, JP-A-50-38543 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") has a mention of the relationship between a crystal form of copper phthalocyanine and its electrophotographic characteristics. Besides copper phthalocyanine, application of metal-free phthalocyanine, hydroxygallium phthalocyanine, chloroaluminum phthalocyanine, and chloroindium phthalocyanine in various crystal forms to electrophotographic photoreceptors have been suggested.
With reference to hydroxygallium phthalocyanine crystals, JP-A-1-221459 refers to the crystal obtained by acid pasting in connection to electrophotographic characteristics.
Reported processes for preparing hydroxygallium phthalocyanine include acid pasting of chlorogallium phthalocyanine with sulfuric acid (Bull. Soc. Chim., France, Vol. 23 (1962)) and hydrolysis using ammonium hydroxide and pyridine (Inorg. Chem., Vol. 19, p. 3131 (1980)).
Hydroxygallium phthalocyanine can be obtained by first synthesizing a halogenated gallium phthalocyanine and then hydrolyzing the resulting halogenated gallium phthalocyanine by acid pasting. Known process for producing chlorogallium phthalocyanine, for example, include (i) reaction between gallium trichloride and diiminoisoindoline (D.C.R. Acad. Sci., Vol. 242, p. 1026 (1956)), (ii) reaction between gallium trichloride and phthalonitrile (JP-B-3-30854; the term "JP-B" as used herein means an "examined published Japanese patent application"), (iii) reaction between gallium trichloride and phthalonitrile in butyl cellosolve in the presence of a catalyst (JP-A-1-221459), (iv) reaction between gallium trichloride and phthalonitrile in quinoline (Inorg. Chem., Vol. 19, p. 3131 (1980), (v) reaction between gallium tribromide and phthalonitrile (JP-A-59-133551), and (vi) reaction between gallium triiodide and phthalonitrile (JP-A-60-59354).
However, electrophotographic characteristics of the hydroxygallium phthalocyanine obtained by acid-pasting hydrolysis of the halogenated gallium phthalocyanine synthesized by any of the known processes are greatly dependent on the process used for synthesizing the starting halogenated gallium phthalocyanine. That is, even with the crystal form being equal, the resulting hydroxygallium phthalocyanine compounds show large variation in performance as an electrophotographic photoreceptor, particularly charging properties and dark decay rate, and it has been difficult to obtain a photoreceptor with stable characteristics.
While various proposals on phthalocyanine compounds have been made to date as described above, it is still demanded to develop phthalocyanine compounds with further improved performance properties.